USDA ARS ARonline Magazine

United States Department of Agriculture

AgResearch Magazine

ARS Home l About ARS l Contact ARS
AR Research Magazine

Subtract Pounds of Weeds,
Add Pounds of Grass = More Cows

Cows: Click here for full photo caption.
An online weed calculator can help researchers estimate how many more cows they could raise per acre if one or two exotic weeds were replaced by forage plants.

An Agricultural Research Service scientist has created an online weed calculator that tells ranchers the number of additional cows they could raise if they eliminated one or two widespread exotic invasive weeds.

Rangeland ecologist Matt Rinella, at the ARS Fort Keogh Livestock and Range Research Laboratory in Miles City, Montana, created a computer model that predicts weed impacts on forage production. Data for developing the model came from 30 weed researchers working throughout the western United States. In addition to developing the calculator so that ranchers can calculate what weeds are costing them on any given site, Rinella used the data to estimate what weeds are costing ranchers in a 17-state region. He calculated that if leafy spurge were eliminated, ranchers in that entire region could graze up to 200,000 more cows per year and save tens of millions of dollars.

Spotted knapweed is another exotic invasive weed whose elimination would greatly increase the number of cows ranches could support, and the calculator also predicts its impacts.

Interested parties can access the calculator at

All the rancher needs is a datasheet, clipboard, pencil, yardstick, and homemade sampling frames of any size, rectangular or circular. The datasheets can be downloaded. Ranchers tally weeds in each frame and group them by height categories. The necessary data can be gathered in about 30 minutes.

After the numbers are entered into the calculator, the ranchers learn how many pounds of weeds they are producing per acre and how many more cattle they could raise per acre if those pounds of weeds were replaced by forage plants.

The calculator reflects a fundamental principle of integrated pest management: It is only worth controlling a pest if the profits from doing so outweigh the costs.—By Don Comis, Agricultural Research Service Information Staff.

Matthew J. Rinella is with the USDA-ARS Fort Keogh Livestock and Range Research Laboratory, 243 Fort Keogh Road, Miles City, MT 59301-4016; (406) 874-8232.

"Subtract Pounds of Weeds, Add Pounds of Grass = More Cows" was published in the April 2010 issue of Agricultural Research magazine.

Share   Go to Top